Interpretive Summary: Currently, there is limited published data relative to the prevalence and antimicrobial susceptibility of Salmonella enterica serovar Agona present in slaughter samples from cattle, chicken, turkey and swine in the US. The objectives of this study were to establish baseline information for S. Agona prevalence in food animal slaughter samples from 1997 through 2003. Salmonella Agona isolates exhibited increased resistance to amoxicillin/clavulanic acid, ampicillin, cefoxitin, ceftiofur, cephalothin, and chloramphenicol, and nalidixic acid. A single isolate was resistant to ceftriaxone. Multiple drug resistance (MDR; resistance >2 antimicrobials) was exhibited in 57% of the S. Agona isolates and 22% of these S. Agona isolates were resistant to 5 or more antimicrobials. A majority of the S. Agona isolates originated from cattle and represented 77% of the MDR isolates resistant to 5 or more antimicrobials. These data will be useful for researchers and policy makers as it suggests that S. Agona is increasing in prevalence in U.S. cattle present for slaughter and should be further monitored.

Technical Abstract:
A total of 499 Salmonella enterica serovar Agona isolates were assayed for antimicrobial susceptibility and subtyped using pulsed field gel electrophoresis. All isolates were collected as part of the animal arm of the National Antimicrobial Resistance Monitoring System - Enteric Bacteria (NARMS) from slaughter and processing samples at federally inspected plants. Isolates originated from cattle, swine, chicken and turkey samples for the years 1997 through 2003. Salmonella Agona isolates exhibited increased resistance to 6 of the 19 antimicrobials tested: amoxicillin/clavulanic acid, ampicillin, cefoxitin, ceftiofur, cephalothin, and chloramphenicol. Although all isolates were susceptible to ciprofloxacin, an increase in resistance to the quinolone, nalidixic acid was observed. A single isolate was resistant to ceftriaxone, however, increased resistance to the other cephalosporins (cefoxitin, ceftiofur, and cephalothin) was observed. Multiple drug resistance (MDR; resistance >2 antimicrobials) was exhibited in 57% (n=282/499) of the S. Agona isolates and 22% (n=111/499) of these S. Agona isolates were resistant to 5 or more antimicrobials. A majority of the S. Agona isolates originated from cattle (40%; n=202/499) and represented 77% (n=85/111) of the MDR isolates resistant to 5 or more antimicrobials. Cluster analysis indicated that isolates did not group together based on the year isolate was recovered, geographical region, or animal source. However, groupings that were indistinguishable by PFGE appeared to correspond with antimicrobial resistance profiles. These data suggest that S. Agona is increasing in prevalence in U.S. cattle present for slaughter and should be monitored further.